Edge following device employing servosystem having bridge with complementary transistors



y 1968 I. D. JOHNSON 3,382,366

EDGE FOLLOWING DEVICE EMPLOYING SERVOSYSTEM HAVING BRIDGE WITHCOMPLEMENTARY TRANSISTORS Filed Jan. 25, 1965 I 2 Sheets-Sheet 1INVENTOR j/myorm ON ATTORNZ/(Z y 1968 l. D. JOHNSON 3,382,

EDGE FOLLOWING DEVICE EMPLOYING SERVOSYSTEM HAVING BRIDGE WITHCOMPLEMENTARY TRANSISTORS Filed Jan. 25, 1965 2 Sheets-Sheet 2 UnitedStates Patent EDGE FOLLOWING DEVICE EMPLOYING SERVO- SYSTEM HAVINGBRIDGE WITH COMPLEMEN- TARY TRANSISTORS Irvin D. Johnson, Littleton,C0lo., assignor to Marathon Oil Company, Findlay, Ohio, a corporation ofOhio Filed Jan. 25, 1965, Ser. No. 427,877 11 Claims. (Cl. 250-202) Thepresent invention relates to devices for the determination of physicaldimensions of objects and for follow ing the edges of objects. Inparticular, the present invention relates to electromechanical opticaldevices for automatically following the edges of objects withoutmechanical contact.

The present invention comprises devices for the following of the edgesof opaque objects, including lines drawn on paper by meanings ofradiation sources, preferably electric lights, detectors so positionedthat the edge of the opaque objects to be followed cut off a portion ofthe radiation which would otherwise fall on said detectors and means forcausing movement of either or both of said detector and said radiationsource so as to maintain substantially constant the amount of light cutoff by said opaque object.

FIGURE 1 is an illustration of the electromechanical components of apreferred embodiment of the present invention.

FIGURES 2 and 2a are illustrations of the electromechanical componentsof other preferred embodiments of the present invention.

FIGURE 3 shows preferred electrical circuitry used in the controllerelement of the present invention.

FIGURE 3a shows a modification of the preferred circuitry for use in aspecialized variation of the present invention.

In FIGURE 1 a cylinder having a somewhat irregular diameter x movesalong its major axis in a direction equivalent to moving out of thepaper. A source of incandescent illumination 22 shines a beam ofradiation 21 upward toward a photocell 23. A carriage 24 slides along aguide bar 26 back and forth in a path approximately perpendicular to themajor axis of the cylinders 20. The carriage is propelled by a screwdrive which is offset from the plane of the light beam 21 so as not tointerfere with the beam. The screw drive is propelled by a reversible DCmotor 27, which is powered through a controller 31 which starts andstops the reverses the motor in response to electrical signals receivedfrom the photocell 23. An adjustable potentiometer 32 is turned so thatno power flows to the motor 27 when approximately half of beam 21 isinterrupted by the object 20. A roller support maintains the left sideof the cylinder 20 in a fixed position. As the cylinde-r becomesnarrower (dimension x decreases), less of beam 21 will be interrupted bythe cylinder and a greater portion of the face of photocell 23 will beexposed to light, thus causing the signal fed by the photocell tocontroller 31 to increase. The controller will then energize motor 27 todrive carriage 24 to the left. As carriage 24 moves to the left, agreater portion of beam 21 will be interrupted by the cylinder 20 andthe signal from photocell 23 will decrease. When this signal decreasesto a preset value, as predetermined by adjustment of variablepotentiometer tap 32, power to the motor 27 will be shut off by thecontroller 31. As the object grows wider (as dimension x increases),more of beam 21 will be interrupted, less of the face of photocell 23will be exposed to light, and the signal from the photocell willdecrease below the preset value. The controller with then sendelectrical current of reverse polarity causing the motor 27 to drivecarriage 24 toward the right, until the signal from photocell 23 onceagain reaches the predetermined value at which point current to motor 27will again be cut off.

Thus, in operation, carriage 24 continuously follows the right edge ofthe cylinder 20. Since the left edge of the cylinder 20 is always heldagainst roller support 30, the position of carriage 24 is proportionalto the thickness x of the cylinder at any point along its major axiswhich is passing through the light beam 21. A sensitive slide-wirepotentiometer 28 mounted in contact with the screw feed 25 continuouslyvaries in resistance in proportion to the position of the carriage 24,and therefore, in proportion to the thickness of the cylinder 20.

The resistance of the slide-wire potentiometer 28 may be digitized, asby, a power supply and a digital volt meter, or recorded as on aconventional linear chart drive recorder coupled with a mechanism whichadvances a cylinder 20 along its major axis, or shown on an oscilloscopeor other display device. Alternatively, the resistance of slide-wirepotentiometer 28 may be run through a time delay and used to operate atrimming tool which grinds or otherwise removes material from thecylinder 20 in order to achieve uniform thickness along its major axis.

FIGURE 2 shows a second preferred embodiment of the present inventionoperating in a manner similar to the embodiment shown in FIGURE 1,except that the light 22 and the photocell 23 are mounted on the sameportion of carriage 24 and the beam from the light projects downwardtoward mirror 29 which reflects the beam upward to the photocell 23.FIGURE 2a shows a further modification which may be made by mounting thephotocell 23 and the light 22 on a wheel 32 connected by gear drive 33which rotates the wheel when it is turned by motor 27. As in thepreviously discussed embodiments, motor 27 is controlled by a controller31 which receives signals from the photocell 23. Slide-wirepotentiometer 28 is moved in relation to the rotation of the wheel 33.

FIGURE 3 shows preferred electrical circuitry for the controller 31.This circuitry is itself inventive, and it is discussed more fully andclaimed in my copending application of the same assignee, Ser. No.420,970, filed Dec. 24, 1964, now abandoned.

The basic elements of the electrical circuitry illustrated in FIGURE 3are a DC power supply 33, a rebalanceable bridge circuit formed byresistance elements R R R and R and a reversible DC motor 27. R is thephotocell 23 shown in FIGURES 1, 2, and 2a, and R is the variablepotentiometer resistance controlled by turning tap 32 shown in FIGURE 1.R and R are fixed resistances. Two pairs of complementary transistorsare connected across two junctions of the bridge. When the resistance ofR (photocell 23) is just sufiicient to balance the bridge, no currentflows to motor 27. When the resistance of R decreases so that the bridgeis unbalanced, a path of current flow from power source 33 is open dthrough transistors 33, 34, 40, 39 and 42 to motor 27 driving the motorin a direction which tends to cause the edge of the object beingmeasured 20 to interrupt a lesser portion of light beam 21. Conversely,when the resistance of R (photocell 23) increases, the current path isopened from the power supply 33 through transistors 35, 36, 38, 37, and41 to drive motor 27 in the opposite direction and cause a greaterportion of light beam 21 to be interrupted.

FIGURE 3a shows a modification which may readily be made to thecircuitry of FIGURE 3. An additional sensing element 23a is substitutedfor fixed resistor R Thus modified, the circuit will respond todifferences in the resistance of sensing elements 23 and 23a. Thismodification is useful where some ambient light falls on element 23,since variations in the intensity of such background radiation can becorrected for by pointing element 23a toward such radiation.

It should also be understood that the devices of the present inventionmay be used in pairs. For example, the roller 30 of FIGURES 1 and 2could be replaced with a second optical caliper system and the outputsfrom both of the slide-wire potentiometer 28 could be algebraicallyadded in a conventional electrical adder circuit so that a thickness ofthe object 20 was continuously measured without any contact whatsoever.In such applications, the object could be hanging rope or extrudedplastic and the invention would be particularly valuable wheremechanical contact would be likely to cause markings where the plastichad not yet hardened. A further variation utilizing a pair of thedevices of the present invention is to mount the devices atapproximately right angles so that their slide wires describe twocoordinates locating the points on the edge of object 20 on a twodimensional grid system. Such a system may be utilized to create anelectro-mechanical pantagraph where the template is followed by the twodevices of the present invention and the output from theirpotentiometers 28 drives a pair of motors which in turn move an arm totrace a pattern geometrically similar to the edge of the template. Inspecialized applications, three devices of the present invention may beutilized so as to locate all three geometric coordinates of points onthe edge of object 20.

It should be understood that while the above specific embodiments haveemployed incandescent radiation, infrared, ultraviolet, nuclear or otherforms of radiation which may be projected in a reasonably directionalbeam may readily be employed with the present invetnion. Further, an ACmotor with phase reversal could be employed. Also, the objects withwhich the invention is utilized need not be solids, but can also beprinted darker or lighter spaces on paper or celluloid, etc. These andother variations of the devices and procedures described are to beincluded within the invention.

The present invention also comprises a bridge-controlled servosysternincluding a reversible motor for maintaining a condition and a desiredvalue comprising a power supply, a motor-controlled circuit connected tosaid power supply, a bridge circuit connected to said power supply andhaving four arms forming four junctions, a transistor switching circuitconnected between two opposite junctions of said bridge and having firstand second outputs connected to said motor control circuit, saidswitching circuit comprising two pairs of complementary transistors,means connecting the base electrodes of the transistors of oneconductivity type of each pair to diiferent forms of said oppositejunctions, and means connecting the base electrode of each of thetransistors of the opposite conductivity type of each pair to theopposite junction different from that to which its complementarytransistor base electrode is connected, condition responsive variableimpedance means in one arm of said bridge for varying electricalpotential at one of said opposite junctions in accordance with acondition, an adjustable impedance means in another arm of said bridgefor adjusting the electrical potential of the other of said oppositejunctions to correspond to a desired value of the condition whereby saidbridge is balanced when the potentials at said opposite junctions areequal so that no signal appears at either of said outputs, and thebridge is unbalanced when said potentials are unequal to provide anoutput signal on a selected one of said outputs as determined by thesense of the bridge unbalance to connect the motor to said power supply,thereby driving said motor in the direction to return the condition tothe desired value to rebalance the bridge and disconnect the motor fromsaid power supply.

Further discussion of the electrical aspects of the present inventionwill be found in the file of US. patent application 420,970 of Irvin D.Johnson, filed Dec. 24,

1964, for Bridge-Controlled Servosystem, now abandoned.

What is claimed is:

1. Electro-optical devices for automatically following the periphery ofobjects substantially opaque to radiation which objects are moving inrelation to the devices, said devices operating without mechanicalcontact with said objects, said devices comprising in combination asource of radiation, a relatively directional radiation detectorgenerating a quantitative electrical signal indicative of the amount ofradiation to which the face of said detector is exposed positioned somedistance from said source, said detector being positioned to receiveradiation from said source and having a substantial area exposed to saidradiation, movable support means for positioning said detector and saidsource in relation to said object so as to expose only a predeterminedportion of said face of said detector to said radiation, reversible andstoppable drive means for moving said support in relation to said objectto alternate positions so as to successively expose greater and lesserportions of the face of said detector to said radiation, a controllerfor operating said drive means in response to said quantitative signalsgenerated by said detector, said controller comprising an electricalbridge circuit connected to a power supply and having four arms formingfour junctions, a transistor switching circuit con nected between twoopposite junctions of said bridge and having first and second outputsconnected to energize said drive means, said switching circuitcomprising two pairs of interconnected transistors, said detectorcomprising a variable impedance electrically connected in one arm ofsaid bridge for varying the electrical potential at one of said oppositejunctions in proportion to the radiation b ing received by saiddetector, and adjustable impedance means in another arm of said bridgefor adjusting the electrical potential at the other of said oppositejunctions to correspond to said preset level of the signal received fromsaid detector, whereby said control means controls said drive means soas to decrease the area of said detector face whenever said bridge isunbalanced by a quantitative signal from said detector which exceeds apreset value which preset value corresponds to the exposure of saidpredetermined area of said detector to said radiation, said controllerstopping said drive means whenever said bridge is balanced by a signalfrom said detector equal to said preset value and said controllerreversing said drive means whenever said bridge is unbalanced by asignal from said detector less than said preset value wherein each ofsaid transistor pairs comprises complementary transistors and whereinthe base electrode of one transistor of each pair of complementarytransistors is connected to one of said opposite junctions and the baseelectrode of the other transistor of each pair is connected to theopposite junction.

2. The devices of claim 1 wherein the drive means comprises a directcurrent motor which is electrically connected to one arm of the bridgecircuit so that said motor and said bridge circuit are powered by asingle direct current power supply.

3. The devices of claim 1 wherein each of said transistor pairscomprises complementary transistors and wherein the base electrode ofone transistor of each pair of complementary transistors is connected toone of said opposite junctions and the base electrode of the othertransistor of each pair is connected to the opposite junction;

4. The devices of claim 1 wherein a second detector is electricallyconnected to an arm of said bridge circuit different from the arm towhich the first of said detectors is connected and wherein said seconddetector is located to sense background radiation, said detectors beingso arranged that said drive means is controlled in response to thedifference between the radiation striking the two detectors.

5. A system comprising two devices of claim 1 in substantially opposedrelationship, each of said devices following a different side of anobject and output means indicative of the relative distance between thedetectors of the devices, whereby the combined signal from said outputmeans is indicative of the thickness of said object.

6. A system wherein a plurality of the devices of claim 1 are utilizedso as to triangulate the locations of points on the periphery of theobject, with the output means providing suflicient information to locatesuch positions on a grid.

7. The system of claim 6 wherein at least three of said devices areutilized so as to provide sufiicient information to locate positions ina three-dimensional coordinate system.

8. A bridge-controlled servosystem including a reversible motor formaintaining a condition at a desired value comprising a power supply, amotor controlled circuit connected to said power supply, a bridgecircuit connected to said power supply and having four arms forming fourjunctions, a transistor switching circuit connected between two oppositejunctions of said bridge and having first and second outputs connectedto said motor control circuit, said switching circuit comprising twopairs of complementary transistors, means connecting the base electrodesof the transistors of one conductivity type of each pair to dilferentforms of said opposite junctions, and means connecting the baseelectrode of each of the transistors of the opposite conductivity typeof each pair to the opposite junction diiferent from that to which itscomplementary transistor base electrode is connected, conditionresponsive variable impedance means in one arm of said bridge forvarying electrical potential at one of said opposite junctions inaccordance with a condition, an adjustable impedance means in anotherarm of said bridge for adjusting the electrical potential at the otherof said opposite junctions to correspond to a desired value of the 3,

condition, whereby said bridge is balanced when the potentials at saidopposite junctions are equal so that no signal appears at either of saidoutputs, and the bridge is unbalanced when said potentials are unequalto provide an output signal on a selected one of said outputs asdetermined by the sense of the bridge unbalance to connect the motor tosaid power supply, thereby driving said motor in the direction to returnthe condition to the desired value to rebalance the bridge anddisconnect the motor from said power supply.

9. A transistor control circuit as defined in claim 8 further comprisinga power supply connected to said bridge circuit and transistors, saidbridge being balanced when the potentials at said opposite junctions areequal so that said transistor pairs are non'conducting, and meansrendering said potentials unequal to balance the bridge whereby one ofsaid transistor pairs becomes conducting while the other remainsnonconducting.

10. A transistor control circuit as defined in claim 9 wherein theemitters of the transistors in each complementary pair are connected inseries.

11. A transistor control circuit as defined in claim 10 wherein when onebridge is unbalanced, the unequal bridge junction potentials cause Onetransistor pair to be forward-biased and the other reverse-biased.

References Cited UNITED STATES PATENTS 1,976,298 10/1934 Richter 2502022,117,878 5/1938 Friedemann 250219 2,674,151 4/ 1954 Garrett et a1250-202 2,273,920 4/1942 Evans et al. 250210 2,810,316 10/1957 Snyder250202 3,204,109 8/1965 Goodwin 250--219 RALPH G. NILSON, PrinmryExaminer.

' M. ABRAMSON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,382,366 May 7, 1968 Irvin D. Johnson It is certified that errorappears in the ahoveidentified patent and that said Letters Patent arehereby corrected as shown below:

Column 1, line 43, "cylinders" should read cylinder line 48, "thereverses" should read and reverses line 70, "with then" should read willthen Signed and sealed this 25th day of November 1969.

@EA Attest:

WILLIAM E. SCHUYLER, IR.

Edward M. Fletcher, Jr.

Cominissioner of Patents Atteating Officer

1. ELECTRO-OPTICAL DEVICES FOR AUTOMATICALLY FOLLOWING THE PERIPHERY OFOBJECTS SUBSTANTIALLY OPAQUE TO RADIATION WHICH OBJECTS ARE MOVING INRELATION TO THE DEVICES, SAID DEVICES OPERATING WITHOUT MECHANICALCONTACT WITH SAID OBJECTS, SAID DEVICES COMPRISING IN COMBINATION ASOURCE OF RADIATION, A RELATIVELY DIRECTIONAL RADIATION DETECTORGENERATING A QUANTITATIVE ELECTRICAL SIGNAL INDICATIVE OF THE AMOUNT OFRADIATION TO WHICH THE FACE OF SAID DETECTOR IS EXPOSED POSITIONED SOMEDISTANCE FROM SAID SOURCE, SAID DETECTOR BEING POSITIONED TO RECEIVERADIATION FROM SAID SOURCE AND HAVING A SUBSTANTIAL AREA EXPOSED TO SAIDRADIATION, MOVABLE SUPPORT MEANS FOR POSITIONING SAID DETECTOR AND SAIDSOURCE IN RELATION TO SAID OBJECT SO AS TO EXPOSE ONLY A PREDETERMINEDPORTION OF SAID FACE OF SAID DETECTOR TO SAID RADIATION, REVERSIBLE ANDSTOPPABLE DRIVE MEANS FOR MOVING SAID SUPPORT IN RELATION TO SAID OBJECTTO ALTERNATE POSITIONS SO AS TO SUCCESSIVELY EXPOSE GREATER AND LESSERPORTIONS OF THE FACE OF SAID DETECTOR TO SAID RADIATION, A CONTROLLERFOR OPERATING SAID DRIVE MEANS IN RESPONSE TO SAID QUANTITATIVE SIGNALSGENERATED BY SAID DETECTOR, SAID CONTROLLER COMPRISING AN ELECTRICALBRIDGE CIRCUIT CONNECTED TO A POWER SUPPLY AND HAVING FOUR ARMS FORMINGFOUR JUNCTIONS, A TRANSISTOR SWITCHING CIRCUIT CONNECTED BETWEEN TWOOPPOSITE JUNCTIONS OF SAID BRIDGE AND HAVING FIRST AND SECOND OUTPUTSCONNECTED TO ENERGIZE SAID DRIVE MEANS, SAID SWITCHING CIRCUITCOMPRISING TWO PAIRS OF INTERCONNECTED TRANSISTORS, SAID DETECTORCOMPRISING A VARIABLE IMPEDANCE ELECTRICALLY CONNECTED IN ONE ARM OFSAID BRIDGE FOR VARYING THE ELECTRICAL POTENTIAL AT ONE OF SAID OPPOSITEJUNCTIONS IN PROPORTION TO THE RADIATION BEING RECEIVED BY SAIDDETECTOR, AND ADJUSTABLE IMPEDANCE MEANS IN ANOTHER ARM OF SAID BRIDGEFOR ADJUSTING THE ELECTRICAL POTENTIAL AT THE OTHER OF SAID OPPOSITEJUNCTIONS TO CORRESPOND TO SAID PRESENT LEVEL OF THE SIGNAL RECEIVEDFROM SAID DETECTOR, WHEREBY SAID CONTROL MEANS CONTROLS SAID DRIVE MEANSSO AS TO DECREASE THE AREA OF SAID DETECTOR FACE WHENEVER SAID BRIDGE ISUNBALANCED BY A QUANTITATIVE SIGNAL FROM SAID DETECTOR WHICH EXCEEDS APRESET VALUE WHICH PRESET VALUE CORRESPONDS TO THE EXPOSURE OF SAIDPREDETERMINED AREA OF SAID DETECTOR TO SAID RADIATION, SAID CONTROLLERSTOPPING SAID DRIVE MEANS WHENEVER SAID BRIDGE IS BALANCED BY A SIGNALFROM SAID DETECTOR EQUAL TO SAID PRESET VALUE AND SAID CONTROLLERREVERSING SAID DRIVE MEANS WHENEVER SAID BRIDGE IS UNBALANCED BY ASIGNAL FROM SAID DETECTOR LESS THAN SAID PRESET VALUE WHEREIN EACH OFSAID TRANSISTOR PAIRS COMPRISES COMPLEMENTARY TRANSISTORS AND WHEREINTHE BASE ELECTRODE OF ONE TRANSISTOR OF EACH PAIR OF COMPLEMENTARYTRANSISTORS IS CONNECTED TO ONE OF SAID OPPOSITE JUNCTIONS AND THE BASEELECTRODE OF THE OTHER TRANSISTOR OF EACH PAIR IS CONNECTED TO THEOPPOSITE JUNCTION.